It is well known to control the timing of ignition, that is, the timing of flash-over of the spark of a sparkplug, as a function of crankshaft angle of the crankshaft to which the pistons of the internal combustion engine (ICE) are connected. The timing of ignition, with respect to crankshaft angle, can be changed in dependence on various parameters and operating conditions of the ICE. An apparatus to control the occurrence of the spark pulse with respect to crankshaft angle is described in the referenced angle U.S. Pat. No. 4,250,858, Jeenicke et al, assigned to the assignee of the present application. This patent describes a system suitable to control the occurrence of the ignition pulse with respect to the crankshaft of the engine.
Usual control apparatus, that is, control apparatus which operates electronically, as well as control apparatus which operates mechanically, as customary in earlier engines, changes the occurrence of the ignition spark with respect to crankshaft angle only when the engine has reached a certain minimum speed, for example a minimum speed close to and just below idling speed. A typical speed in vehicular-type ICEs, for example, as used in passenger automobiles, is about 600 rpm. Mechanical ignition timing elements usually do not respond at all below that minimum speed. What has been done, customarily, is to set the occurrence of the ignition pulse with respect to a few degrees of crankshaft angle in advance of upper dead-center (UDC) piston of a position in a cylinder. In electronic incremental, or segmental control systems, as described, for example, in the referenced U.S. Pat. No. 4,250,058 and, also, in the referenced "Bosch Technical Reports", Vol. 5, pp. 250-256, change of occurrence of the ignition pulse with respect to crankshaft angle is possible only within a very restrictive angular extent, so that, below a certain speed, the ignition occurrence was controlled to a fixed angle with respect to crankshaft rotation.
During starting, customary automotive-type ICEs are driven at speeds which may reach up to 250 rpm--that is, substantially below the idling speed. Fixed setting of ignition angle with respect to crankshaft rotation which is suitable for idling speed or for a minimum speed of about 600 rpm is not optimal at the starting speed. The duration of combustion of the fuel-air mixture within the combustion chamber of the ICE is, usually, about two milliseconds. The maximum pressure within the combustion chamber of the cylinder, at lower and lower speed, thus will occur earlier--with respect to UDC position of the piston--which, with increasing compression, may lead to knocking or pinging, and starting difficulties.